it also lists gwylad as gwyl + ad. merry, glad or lively from 10th century guiillat - hilaris.
So to me partying or going wild at night fits as well.
In the next line she said a lot of cross words and in the last line she nearly broke his heart.
To me his cariad is a bit of a party girl with a gob on her who is tearing his heart apart?
PS I work ar ben waun Tredegar as it now happens, hence my interest in the song. Well I say that I work on waun Tredegar but no-one ive asked seems to know where the waun is - there are three potentially - there are wauns to the North, east and west of the town.